Certificate of correction



Aug. 11, 1959 H. I. CHAMBERS OSCILLOGRAPH APPARATUS Filed June 25, 1956 1 l8 RECORD/N6 I AMPLIFIER MIXER OSCILLATOR MOTOR m PREAMPL/F/ER v28 INPUT SIGNA L VAR/ABLE SPL E D FIG. 2.

INVEN TOR. HERBERT CHAMBERS A TTOPNE VS United States Patent OSCILLOGRAPH APPARATUS Herbert 1. Chambers, Pasadena, Calif., assignor to Consolidated Electrodynamics Corporation, Pasadena,

Calif., a corporation of California Application June 25, 1956, Serial No. 593,671

2 Claims. (Cl. 346-69) This invention relates to a direct recording oscillograph, and more particularly, is concerned with improvements in a string galvanometer for recording an oscillographic trace directly upon a recording medium.

Direct writing oscillographs utilizing a string galvanometer have heretofore been proposed in which the writing element is a movable conductor constituting the string of the string galvanometer. The tring is supported at its two ends so that its central portion can be deflected transversely a relatively large distance in either direction to provide the large amplitudes of motion which are required for recording directly. For direct writing on current-sensitive recording paper, such direct recording string galvanometer type oscillograph includes an anvil having an edge located at the central portion of the string which guides the recording paper past the center of the string. The edge of the anvil is perpendicular to the string, and the current-sensitive paper is moved over the edge of the anvil so that it passes between the anvil and the string. Suitable means are provided for urging the string against the paper where the paper passes over the edge of the anvil, and a source of current is coupled between the paper and the string so that an electric current passes between the paper and the string at the intersection of the string and the line formed where the recording paper passes over the edge of the anvil. The current density at the point of contact between the paper and the string is sufiiciently high to turn the paper black at that point. Thus a trace is formed on the paper which provides a record of the deflections of the string in response to an applied signal. This type of recording oscillograph is described in co-pending application Serial No. 461,088, filed October 8, 1954, in the name of Lewis B. Browder.

Because the restoring force on the string is very slight, intermittent sticking, or stiction as this phenomenon is sometimes referred to, between the recording paper and the galvanometer string produces nonlinearity in the trace with very low frequency or slowly varying D.C. signals. These nonlinearities become particularly marked and therefore are particularly objectionable where the rate of travel of the recording medium is quite slow, as is usually the case where low frequency or DC. signals are being recorded.

According to the present invention an improved oscillograph is provided utilizing the conductor of a string galvanometer as the recording element by the provision of means for overcoming the stiction existing between the recording element and the recording medium. This is accomplished by injecting a high frequency low amplitude voltage on the galvanometer string to make it vibrate slightly. This vibration keeps the string in constant motion at relatively high velocity preventing a static friction condition from existing between the string and the recording medium.

In brief, the oscillograph of the present invention comprises means for producing a magnetic field in which a defiectable conductor is positioned with the conductor ICC the strip may be held in contact with the conductor along a line. Means is provided for passing a signal current through the conductor in response to an input signal, whereby the conductor is deflected in the magnetic field, producing a trace on the recording medium indicative of the variations in the input signal as a function of time.

An oscillator having a frequency higher than the normal operating range of the oscillograph is provided, the oscillator being coupled across the conductor to cause the conductor to vibrate continuously at the frequency of the oscillator.

For a better understanding of the invention, reference should be had to the accompanying drawings, wherein:

Fig. 1 is a fragmentary, partially schematic elevation of one embodiment of the invention; and

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1. Referring to the drawings in detail, the numeral 10 in dicates the string element of the galvanometer which comprises afiexible conductor supported at its ends by a pair of springs 12 and 14. The springs are arranged to provide resilient support for the string element along the direction of the string, and they serve to restrain movement in all other directions so that the deflection of the string is not adversely afie'cted by the end supports. These springs are mounted at spaced positions on a frame member, indicated generally at 16, which is made of suitable non-magnetic material. I

A magnetic pole piece 18 and a pair of members 20 and 22 forming a second pole piece are located on op'posite sides of the string element 10 to provide a magnetic field which extends at right angles to the string element; The upper pole piece is in two parts to permit a recording medium, such as a strip 25 of current-sensitive recording paper, to pass between the two members 20 and 22 into contact with the string element 10 of the galvanometer.

A conductive guide or anvil 24 is located in the space between the two members of the upper pole piece over which the strip of recording medium passes. The anvil has an edge which extends at right angles to the string element iii. A potential is maintained between the string element and the sensitive surface of the paper by means of a battery 26 connected to the string element 10 and to wiper contacts 27 that engage the surface of the strip 25. Current flowing through the current-sensitive recording paper at the intersection between the string element and the line formed by the edge of the conductive anvil 24 causes a trace to be recorded on the paper in accordance with the movement of the string element 10.

An input signal is applied across the ends of the galvanometer string 10 by means of a preamplifier 28, a mixer 30, and a recording amplifier 32. Thus variations in the input signal produce variations in the current flow through the galvanometer string, the flow of current through the string causing a deflection of the string by virtue of the magnetic field in which the string is immersed. By proper shaping of the magnetic pole pieces, the flux distribution can be arranged to produce a substantially linear relationship between the amplitude of deflection of the string and the amplitude of the input signal.

The recording strip moves from a supply reel 34 to a take-up reel 36 after passing over a pair of guide rollers 38 and the anvil 24. The take-up reel 36 is driven by a motor 40 through a suitable variable speed drive mechanism 42 which is preferably of a type described in c0- 3 4 pending application No. 510,433, filed May 23, 1955, in the name of Herbert 1. Chambers.

Because of the relatively small restoring force produced on the galvanometer string by means of the springs 12 and 14, contact friction between the galvanometer recording strip produces a striction effect, i.e., an intermittent stick and slip condition between the paper strip and the string. This striction effect causes a chattering or jumping of the galvanometer string as it is deflected over the surface of the paper, producing errors in the resulting trace. To overcome the striction effect, an oscillator 44 is provided, which may be any suitable type of audio-oscillator capable of oscillating in the frequency range of 1000 cycles. The output of the oscillator 44 is coupled to the mixer 30 through a relayoperated switch 46, whereby a relatively high frequency signal is applied across the galvanometer string to cause it to vibrate. The frequency of the oscillator 44 is not critical, but is chosen to be above the normal operating range of the galvanometer which has an upper limit of the order of 500 cycles. The amplitude of vibration of the galvanometer string may be made quite small, of the order of twice the normal trace width, for example, of the order of .010 of an inch.

Since the striction efiect between the galvanometer string and the recording paper is most pronounced at low paper transport speeds, the relay-operated switch is controlled in response to the variable speed drive 42. Particularly, the preferred variable speed drive 42 includes a plurality of push button controls 47 for setting the desired tape transport speed. One or more of these push buttons at the low speed end of the adjustable speed range may be made to operate switches, such as indicated at 48, which connect a potential source 50 to the relay switch 46, whereby the oscillator 44 is coupled to the mixer 30 when the low tape speeds are selected by the push buttons in the variable speed drive 42.

From the above description it will be recognized that an improved oscillograph is provided which gives greater accuracy at low recording tape speeds by vibrating the 4 galvanometer string to keep it in constant motion. The only eifect on the trace produced by the galvanometer string is to produce a slightly heavier line on the recording paper. This has the added advantage that it improves trace density without incurring the risk of burning the paper at low paper speeds, as would result from increasing the writing current density.

What is claimed is:

1. An oscillograph comprising means for producing a magnetic field, a defiectable conductor, means for supportably positioning the conductor in the magnetic field with the conductor extending in a direction transverse to the direction of the magnetic field, an elongated strip of flexible recording medium, means for moving the strip past the conductor, a portion of the conductor being in rubbing contact with the strip, means for imprinting the strip on contact therewith by the conductor, means for passing current through the conductor in response to an input signal, an oscillator having a frequency higher than the normal operating range of the oscillograph, and means for coupling the output of the oscillator across the conductor, whereby the conductor is caused to vibrate continuously at the frequency of the oscillator.

2. Apparatus as defined in claim 1 wherein said means for moving the strip includes means for adjustably varying the speed of the strip to a plurality of predetermined values, and means controlled by said speed adjusting means for limiting the application of the oscillator out put to the conductor to the slower strip speeds.

References Cited in the file of this patent UNITED STATES PATENTS 626,848 Wills June 13, 1899 1,076,445 Orling Oct. 21, 1913 1,820,088 Parker et al Aug. 25, 1931 1,958,696 Digby May 13, 1934 2,433,382 Morrison Dec. 30, 1947 2,775,503 Peterson a. Dec. 25, 1956 2,827,610 'Hiser Mar. 18, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,89%259 August 1]., 1.959

Herbert Chambers I It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, lines 6, 8, 11, and 25, for "striction", each occurrence, read stiction Signed sealed this 16th day of February 1960 (SEAL) Attest:

KARL PL AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION I Patent Noo 2,899,259 August ll, 1959 Herbert g, Chambers It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 3,- lines 6, 8,11, and 25, for "striotion", each occurrence, read em stiction Signed sealed this 16th day of February 1960.,

(SEAL) Attest:

KARL H, AXLINE 5 ROBERT C. WATSON Attesaing Ofiicer Commissioner of Patents 

